The use of alternating current and direct current in the same electrical system poses a number of problems. In short, these are: circuit and hardware enclosures, outlets, wiring diagrams and sizes, and switches.
The electrical code prohibits alternating and direct current in the same box. You will need two distribution boxes – one for the AC and one for the DC.
Circuit breakers designed for alternating current will not work for direct current. Expect to pay more for DC breakers. On the other hand, fuses are generally indifferent to alternating or direct voltages, or even to voltage differences. Old style circuit boxes using fuses that no longer meet the code for AC wiring will work fine for DC circuits. Up to 30 amps, the new style of automotive fuse is also suitable for DC systems.
Standard outlets will operate on either direct or alternating current. You should be careful using both in the same household. If you plug a 12V DC load into a 120V AC outlet, you risk frying it if the circuit breaker/fuse does not blow first
Connecting a 120 VAC load to a 12 VDC circuit may injure the load, blow a fuse, or do nothing. Yet who needs this worry. Amateur electricians have a lot of
ways to handle this situation. A schematic uses the same type of receptacle for both AC and DC circuits but color codes or labels on the receptacle plate itself. It works well for hermits, but it’s ugly for guests, kids, and the uninformed.
A second system consists of plugging the alternating current and the direct current in the same receptacle, with a common bad idea ). Another solution is to connect the 12V devices to a single automatic cigarette.
lighter grip/grip (light loads only, please). Or a plug/socket of the style found in older recreational vehicles (recreational vehicles) for 12V circuits (mostly insufficient).
A better idea is to use a plug with a different NEMA number (model) for the 12V circuit (look for the cheapest type). This usually changes the orientation of the pins on the plug so that it is not possible to mix 12V DC and 120V AC loads and circuits. Add the appropriate plug to each 12V load.
Polarity is another issue with DC. Incandescent lamps and simple heating circuits don’t really care about polarity, but you have to stick to the polarity (pos. Or neg.) Of LEDs, high frequency fluorescent lights, stereos and many other loads CC. This is easily handled by the new style of plugs and sockets which only allow insertion one way. These ensure the correct polarity of the wiring plug and socket, as well as the use of 3-pin plugs.
Overall, 12V DC wiring will require a higher wire gauge for even modest loads. The wire size increases rapidly regardless of the length. Here, preparation and creativity go a long way
towards minimizing expense and labor while retaining all abilities.
What do you want to do and where? Special low voltage wiring boards will help you size wires for specific loads at varying distances
There is also merit in the idea of directing a heavy wire service line to the far side of the house where it can be distributed from a second, smaller fuse box to loads in that area. caliber is rigid and difficult to transport; plan accordingly. Use “fingers” of 12 gauge wire from a larger gauge wire to facilitate connections to outlets and switches.
Use junction boxes for 8 gauge or larger wire. Relatively short lengths of # 12 wire leading therefrom to loads and receptacles will cause only small losses.
Switches designed to handle 120 V AC may fail when used with 12 V DC. The arc produced when a standard AC switch opens (turns off), a DC circuit will be hotter and last longer.
Absolutely avoid “silent” types of switches; they open too slowly. Either way, the DC arc will eventually (if not immediately) burn out the contacts of a switch. It is possible to add a capacitor on the switch to remove this arc.
Or to wire a multi-pole switch in series to help it survive this arc. Of course, you can also find and install switches designed to switch direct current.